A court in Sudan has upheld the death sentence of four Islamists convicted in June of killing an American diplomat and his Sudanese driver in January 2008. The diplomat's mother in the United States had asked the court to uphold the previous ruling.

Four Islamists, convicted of killing American diplomat John Granville last year in the Sudanese capital, were sentenced to death by hanging after a court upheld their death sentences.

Judge Sayed Ahmed Al-Badry recited quotes from Islamic texts denouncing killing Muslims and non-Muslims. He said it is a great sin to take another person's life. After the judge announced his verdict, the men called Granville an "infidel" and said Muslims should not be executed for killing non-believers.

Granville, who was working for the U.S. Agency for International Development, was killed with his Sudanese driver, Abdel Rahman Abbas. The two men were shot in the early hours of 2008 after a New Year's Eve Party.

The death sentence for the four convicted men was originally passed in June. But under Sudan's Islamic law, the family of a murder victim can request the death penalty for those convicted, forgive them, or ask for compensation. According to media reports, some members of Abbas' family had pardoned the killers.

But on Sunday, a letter from Granville's mother in the United States was read out to the court in which she specified that she wanted the four men to be executed.

Granville's lawyer, Taha Ibrahim, says the court has made a just ruling.

"Her wish was to apply death by retribution and the court accordingly passed death sentence by hanging," Ibrahim said. "It is the legal sentence, it is proper, it is according to the law and it will be executed."

The four men have maintained their innocence, saying they had been convicted in a political trial and that their videotaped confessions were extracted under torture. They have 15 days to appeal the verdict.